1. Field of the Invention
The present invention relates to polymer-bonded perylene dyes and compositions such as, e.g., printing inks which comprise polymer-bonded perylene dyes as colorants.
2. Discussion of Background Information
Counterfeiting and market diversion of mass produced goods are facilitated if the products are handled on a lot base rather than on an individual item base. In such case counterfeit or diverted products are easily introduced into the supply chain. Producers and retailers would like to be in a position to distinguish their original products from such counterfeit or diverted (parallel imported or smuggled) products at the level of the individual unit that is sold.
Further, secure documents such as currency, passports, or identity cards are increasingly counterfeit around the world. This situation is a very critical issue for governments and society in general. For example criminal organizations may use fake passports or identity cards for human beings traffic. As reprographic technologies become more and more sophisticated, it becomes even more difficult to make a clear distinction between a fake document and the original. Document security has therefore a considerable impact on the economy of the countries and also on the victims of illicit traffic involving counterfeit documents.
In an attempt to prevent counterfeiting marking is currently used extensively for the recognition, identification and authentication of individual items. The marking may be applied, for example, in the form of indicia such as 1-dimensional barcodes, stacked 1-dimensional barcodes, 2-dimensional barcodes, 3-dimensional barcodes, a data matrix. and the like. The application of markings is frequently carried out by a printing process which uses a printing ink with specific optical properties that are imparted to the ink by one or more substances contained therein such as, e.g., luminescent dyes and pigments and cholesteric liquid crystal compounds.
A class of compounds which is suitable for use in, e.g., printing inks for marking purposes are perylene dyes. The parent compound perylene displays fluorescence and there are many derivatives of perylene which are known and may theoretically be employed as colorants in compositions for marking such as printing inks and the like. However, a drawback of perylene dyes is their often unsatisfactorily low solubility or dispersibility in liquid media such as those which are useful in printing inks. This low solubility/dispersibility limits the suitability of perylene dyes as colorants for liquid compositions in general. It would thus, be advantageous to be able to increase the solubility and/or dispersibility of perylene dyes in liquid media and in particular, liquid media for use in printing inks.